1. Field of the Invention
The present invention relates to a method for detecting a defect in a prepit sampled when a control operation is performed by using a sample servo (discrete block servo) system in an optical disk drive unit, a magnetooptic disk drive unit, etc.
2. Description of the Related Art
In an optical disk drive unit or a magnetooptic disk drive unit, focusing and tracking controls, etc. are performed by using an optical or magnetooptic disk as an information recording medium and a sample servo system when information is recorded and reproduced. In a tracking system of the above sample servo system, prepits for sampling are formed on a recording face of the information recording medium. A tracking signal is produced by using a wobble mark of prepits and a synchronization signal is produced by using a clock mark of another prepit so as to preform a synchronizing operation in a PLL control.
However, when the focusing and tracking controls are performed by the sample servo system and there is a defect in a prepit, a tracking shift is caused and the PLL is incorrectly operated when sampling data in this defective prepit portion are used as they are.
Accordingly, it is necessary that such incorrect sampling data are not inputted. Therefore, the detection of a defect in a prepit is an important subject.